In order to observe objects or images of objects disposed in vacuum chambers, it is necessary to either insert the observation lens and the sensor (camera) into the vacuum chamber or to observe the objects or images through a vacuum window.
This is particularly required in the case of images using extreme ultraviolet radiation (EUV) if this radiation is converted using scintillators into radiation of a different wavelength and then reproduced on the sensor using additional optics such as described in U.S. Pat. No. 5,498,923.
If the sensor is disposed in the interior of the vacuum chamber, this leads to gas emission of, for example, siloxanes or hydrocarbons from the sensor. This poses a high hazard of contamination of the devices disposed in the vacuum chamber. Optical elements that are exposed to radiation that is rich in energy, particularly EUV radiation, are especially at risk.
If the sensor is disposed outside this vacuum chamber, the radiation used for the image must be guided through a vacuum window onto the sensor. As a result of the window in this case, limitations arise with respect to the quality of the optical images and the usable aperture of the imaging optics.